could someone explain to me the difference between these 2? and when i would need to use them?

thanks

When you use post-fader (the default setting), the signal is first routed through the fader and then to the aux bus. Which means, that the fader controls not only the volume of the channel, but also the amount of signal which is send to the aux bus.
When you use pre-fader, 100% of the signal will be sent to the aux bus anyway, no matter at which possition your fader is. for example: When you have a reverb on your bus as a send effect and set the sends to pre-fader, you can hear the reverb of this channel even when the fader is totally pulled down. In this case you would even ONLY hear the reverb.

thanks for your help i understand it now.